Modern wireless receiver design relies heavily on calibration to achieve desired performance. Calibration is often implemented to adjust operating conditions based on circuit performance. It reduces the need for over design to meet performance across statistical variation in circuits. For example, gain calibration can be employed to keep receiver gain relatively constant across operating conditions.
Modern wireless receivers are typically implemented in integrated circuits. Including dedicated calibration structures in such integrated circuits incurs costs in terms of die area, design resources and test inputs. In particular, the test inputs for use in a factory calibration setting can prove expensive. Therefore, it is desirable to employ power-on calibration or periodic self-calibration techniques as much as possible.
In receiver RF front ends, cascaded gain is a strong function of device transconductance, and varies with performance corners and temperature. Similarly, for receivers with very narrowband response, band response is dependent on capacitor and inductor sizes, and can vary with corners as well as model inaccuracy. Therefore, accurate calibration is required in such receivers to ensure the response is centered in the desired frequency band and gain, especially when the receivers have a very narrow bandwidth response.
Among existing techniques for gain calibration and band tuning, a frequency-sweeping input tone with a known power level can be applied to the receiver input while monitoring the output of the receiver. This method is very straightforward and provides gain and band tuning information in the same test. However, providing a frequency-sweeping input tone can be very expensive during factory calibration.
A modification of the above method can use an on-chip local oscillator signal as a test input. However, routing the local oscillator test signal to a low noise amplifier input may be a design concern. Moreover, calibration becomes less robust due to potential for change in local oscillator power.
Another approach for band tuning is to use similar inductors for the low noise amplifier and voltage control oscillator (VCO) and derive band tuning information from the VCO tuning code. This method constrains the low noise amplifier inductor size and may not provide adequate accuracy.
It would be desirable to be able to accurately calibrate front end filters while overcoming the shortcomings of traditional approaches.